1. Field of the Invention
The invention relates to an ink supplying device which makes it possible to apply negative pressure to ink to be supplied into a print head, without use of a device for adjusting ink supplying pressure.
2. Description of Related Art
Conventionally, in an ink jet printer, ink supplied to a print head is jetted out from multiple nozzles to perform printing. In such a printer, in order to maintain the quality of printed results, it is necessary to keep a jetting ability of the ink jetted out from the print head. The ink jetting ability is kept by making the liquid surface of the ink supplied into the nozzle in the print head into a meniscus (curved surface) in a concave form. The ink liquid surface in a meniscus form is formed by adjusting the ink supplying pressure for the ink supplied into the nozzle of the print head into a negative pressure.
The ink supplying pressure is adjusted by a difference in level between the ink print head and the ink package. When the ink package is arranged, for example, near and below the print head, the difference in level between the ink package and the print head occurs so as to cause a difference in the head of negative pressures. By such a difference in the head of negative pressures, the ink supplying pressure is adjusted into a negative pressure. However, in general a feeding mechanism for feeding printing paper and other devices are disposed below the ink head, and consequently the position and the space for disposing an ink package are limited. Accordingly, in order to dispose an ink package at the limited position or space, it is necessary to make the capacity of the ink package small and frequently exchange the ink package.
Thus, a method is proposed that a small-sized sub-tank is arranged near and below an ink head and an ink package having a large volume is separately arranged as a main tank at a desired position. According to this method, the ink inside the ink package is supplied to the sub-tank arranged near and below the print head by pumping it up, and the ink supplied into the subtank is supplied into a print head under the condition that its ink supplying pressure is adjusted into a negative pressure. Since such a small-sized tank has a small capacity, it can be easily arranged near and below the print head. Furthermore, the volume of the ink package does not have to be downsized, since it is separately arranged at a desired position.
However, according to the adjustment of the ink supplying pressure using the above-mentioned sub-tank, it is necessary to use the sub-tank for adjusting the ink supplying pressure into a negative pressure, and a pumping device for pumping up ink from the ink package to the subtank. Therefore, the number of the parts of the printer increases, and the size of the printer becomes large, which increases the cost for manufacturing the printer. Also, electric power for driving the pumping device becomes necessary, which increases the consumption of electric power of the printer.
On the other hand, in an ink jet printer which is capable of carrying out color printing, inks of four colors including black, yellow, cyan, and magenta are jetted out from multiple nozzles to perform color printing. In such a printer, to maintain good printing quality, it is necessary to maintain a uniform ink jetting ability for the respective inks jetted out from a printer head. The ink jetting ability is maintained uniform by forming the liquid surface of the ink supplied into the nozzle of the printer head into a concave meniscus (curved surface). The ink surface is formed into a meniscus form, for example, by adjusting the ink supplying pressure for the ink to be supplied into the nozzle of the printer into a negative pressure within a specific range. Therefore, it is possible to keep the ink jetting ability for the respective inks uniform by maintaining the ink supplying pressures substantially equal for the respective inks.
The ink supplying pressure is adjusted by a difference in level between the ink head and ink packages in which the inks of the respective colors are disposed. For example, the respective ink packages are adjacently arranged near and below the printer head and at substantially the same levels so as to make level-differences of the printer head from the respective ink packages substantially equal. By arranging the respective ink packages as described above, it is possible to create a substantially equal negative pressure inside the respective packages because substantially equal potential head (energy) differences are generated between the printer head and the respective ink packages.
In the above-mentioned printer, in order to provide a space where the respective ink packages are adjacently arranged in the horizontal (lateral) direction, it is necessary that the length in the lateral direction of the printer is long. However, when the printer that has a long length in the lateral direction is set on a desk or other piece of furniture, the majority of the surface of the desk is occupied by the printer. This is not preferable. Thus, it may be considered that the multiple ink packages are not arranged in the horizontal direction, but are stacked in the vertical direction. This makes it possible to make the length in the lateral direction of the printer short, and consequently the printer-setting area is reduced. Thus, a working space on the desk or other piece of furniture can be effectively used.
However, in the case of stacking the ink packages in the vertical direction, a larger positive pressure is applied to the upper ink package than the lower ink package because of the difference in potential head (energy) between the upper and lower ink packages when ink is extracted from the upper ink package. Thus, the ink supplying pressures in the respective ink packages are not balanced. For this reason, the ink jetting ability for the respective inks cannot be made to be uniform which creates the problem that good printing quality cannot be maintained.